Apple has done a remarkable job moving the Mac from 68K to PowerPC to x86 to ARM over the course of three decades.

Their latest static-translation based emulator (Rosetta2) is pretty cool as well.

The CPU world seems like it was a lot more interesting in the early 1990s, with Apple creating native versions of Mac OS for 68K, x86, and PowerPC – and running Mac OS in emulation on 29K and 88K (on Apple hardware prototypes) as well as on SPARC, POWER, and PA-RISC (on Sun/IBM/HP workstations.)

Shame that Apple didn't try making an ARM-based Mac back then as well - though they did use ARM chips in the Newton.